For colonoscopy prep, low-volume, same-day dosing appears as effective as split dosing

A randomized trial of three polyethylene glycol regimens found that more patients tolerated and were willing to repeat low-volume same-day or split-dose prep compared to high-volume split-dose regimens.


Low-volume, same-day colonoscopy prep resulted in similar bowel cleanliness compared with high-volume or low-volume split dosing, according to a large randomized industry-funded trial of polyethylene glycol (PEG) regimens.

At 10 Canadian endoscopy units, researchers allocated patients undergoing colonoscopies between 10:30 a.m. and 4:30 p.m. to low-volume same-day (15 mg of bisacodyl the day before and 2 L of PEG the morning of the procedure), low-volume split dose (15 mg of bisacodyl the day before and 1 L of PEG plus 1 L of PEG the morning of), or high-volume split dose (2 L of PEG the evening before plus 2 L the morning of). The primary endpoint was bowel cleansing score rated by a blinded endoscopist using the Boston Bowel Preparation Scale. Patients' tolerability of the prep method was assessed by a validated questionnaire measuring willingness to repeat the procedure and a Likert scale from 1 to 10 that rated tolerability and symptoms. Results of the study, which was funded by the manufacturer of the bowel preparations, were published July 29 by The American Journal of Gastroenterology.

The proportions of patients with adequate bowel cleanliness were not significantly different across the three groups: low-volume same-day (90.5%), high-volume split dose (92.2%), and low-volume split dose (87.9%). Results did not change after adjustment for patient demographic characteristics and time elapsed from end of preparation to colonoscopy. Patients' willingness to repeat the preparation was not significantly different between the low-volume same-day and low-volume split-dose groups (91% vs 92.5%; P=0.395) but was lower in the high-volume split-dose group (68.9%; P<0.01). Bowel preparation was better tolerated in the low-volume same-day group (8.1±1.9) compared with the high-volume split-dose group (7.3±2.3; P<0.01) but not significantly different compared with the low-volume split-dose group (8.2±1.9; P=0.65).

Compared with the low-volume same-day dose, the high-volume split dose was associated with a greater incidence of unpleasant taste, bloating, headaches, dizziness, and chills. Compared with the low-volume same-day dose, the low-volume split dose was associated with a greater incidence of unpleasant taste, bloating, and dizziness, but less perianal irritation. No significant differences were seen between preparations for withdrawal time, cecal intubation, or polyp detection rates.

“Although there were no primary outcome differences in efficacy between the low-volume same-day and the high-volume split-dose regimens, the former was significantly better tolerated and more patients were willing to repeat the preparation,” the authors wrote. “There were no significant differences in tolerance or willingness to repeat between low-volume same-day and the low-volume split dose.”